I haven’t seen much about this but I assume the passport systems are a potentially huge security risk. The ones I’ve seen require personal identifying information (yet again) which you know is stored in a new database (again).
The (european) vaccination certificates include all necessary information in a QR code that is stored locally, either digitally in an app or as actual print-out of the QR code. You only have to show an id card to proof that this QR code belongs to you then (it also encodes your full name and date of birth for making the connection).
Other countries that have nationwide systems should have been able to do something similar - of course there's a good chance they didn't, but that's really not an argument against Covid passports but against bad security practices.